Fixed evaluation of the disable-build-docs argument.
Fixed evaluation of the disable-build-docs argument.

Now at least enable_build_docs is set correctly.

stapelberg/libxcb,OpenInkpot-archive/iplinux-libxcb,stapelberg/libxcb,topcat/xcb-win32,stapelberg/libxcb,topcat/xcb-win32,topcat/xcb-win32,OpenInkpot-archive/iplinux-libxcb,topcat/xcb-win32,topcat/xcb-win32,OpenInkpot-archive/iplinux-libxcb